1. Field of the Invention
This invention relates generally to patterned perpendicular magnetic recording media, such as disks for use in magnetic recording hard disk drives, and more particularly to patterned perpendicular disks with ultra-high data densities.
2. Description of the Related Art
Magnetic recording hard disk drives with patterned magnetic recording media have been proposed to increase data density. In conventional continuous magnetic recording media, the magnetic recording layer is a continuous layer over the entire surface of the disk. In patterned media, also called bit-patterned-media (BPM), the magnetic recording layer on the disk is patterned into small isolated data islands arranged in concentric data tracks. Patterned-media disks may be longitudinal magnetic recording disks, wherein the magnetization directions are parallel to or in the plane of the recording layer, or perpendicular magnetic recording disks, wherein the magnetization directions are perpendicular to or out-of-the-plane of the recording layer. Perpendicular media will likely be the choice for patterned media because of the potential for increased data density. To produce magnetic isolation of the patterned data islands, the magnetization of the spaces between the islands is destroyed or substantially reduced to render these spaces essentially nonmagnetic. Alternatively, the media may be fabricated so that that there is no magnetic material in the spaces between the islands.
One problem associated with patterned perpendicular media is a wide distribution of the switching field, i.e., the write field required to switch the magnetization of an island from one magnetic state to the other state. Ideally the switching field distribution (SFD) width would be zero, meaning that all the islands would switch at the same write field strength. A high-width SFD increases the likelihood of the write field switching the magnetization of islands adjacent to the island being addressed, i.e., “overwriting” of previously written data. One significant contribution to a high-width SFD is the magnetostatic coupling of neighboring magnetic islands due to the interactions of dipolar fields from adjacent islands.
Patterned perpendicular disks have been proposed with ultra-high areal bit densities (at least 1 Terabits/in2). However, the adverse effect of magnetostatic coupling becomes more pronounced as the spacing between the islands decreases, which occurs as the areal bit density of the patterned media increases. Ultra-high areal density may also cause an additional problem. Due to the high write field and limited head field gradients achievable there may be fringing fields from the write head leaking into adjacent islands, which can cause overwriting. This problem is exacerbated because the fringing fields acting on adjacent islands encompass relatively large angles with the perpendicular easy-axis of the recording layer on the islands, which increases the likelihood of overwriting.
Patterned perpendicular disks have been proposed primarily for use in conventional magnetic recording, wherein an inductive write head alone writes data to the islands. However, patterned perpendicular disks have also been proposed for use in heat-assisted recording, also called thermally-assisted recording (TAR). In a TAR system, an optical waveguide with a near-field transducer (NFT) directs heat from a radiation source, such as a laser, to heat localized regions of the magnetic recording layer on the disk. The radiation heats the magnetic material locally to near or above its Curie temperature to lower the coercivity enough for writing to occur by the inductive write head.
What is needed is an ultra-high areal density patterned perpendicular disk, usable in both conventional recording systems and TAR systems, with data islands less susceptible to the adverse effects of magnetostatic coupling and fringing fields.